The present invention relates to a battery management system for a battery having a plurality of battery cells connected in series, the battery management system comprising a battery control unit, a plurality of low-voltage measuring devices, by means of which the voltage of one or more battery cells can be measured in each case, and comprising at least one of the following components: one or more high-voltage measuring devices for a voltage across a plurality or all the battery cells, at least one current measuring device, by means of which a current from or through the battery can be measured, and at least one measuring module comprising a high-voltage measuring device and a current measuring device. The invention further relates to a battery and a method for measuring a plurality of low voltages of either individual battery cells or groups of a plurality of battery cells by means of a plurality of low-voltage measuring devices and for measuring a high voltage of a plurality or all of the battery cells with a high-voltage measuring device. High voltages cannot be measured using low-voltage measuring devices without additional measures. Voltages are designated here as high voltage which exceed the voltage of one or several battery cells connected in series. According to a conventional, general definition, these are DC voltages over 60 V and AC voltages over 25 V. The term is used in the field of electric vehicles. Lesser voltages are denoted as low voltages in this patent application.
In the prior art, additional system voltages, typically high voltages, such as, for example:                the high voltage of a plurality or all of the battery cells,        intermediate circuit voltages,        vehicle electrical system voltages of charging apparatuses,        system voltages of low-voltage-high voltage-DC-DC converters,are measured and monitored by a microprocessor system in a battery management system for electric and hybrid vehicles, in particular for the use with lithium ion cells, in addition to low voltages, such as individual cell voltages. Voltages from a high-voltage section of the battery or respectively systems connected thereto can be measured via a high-voltage section of the battery control unit, and corresponding measurement data can be transmitted in an electrically isolated or respectively galvanically separated manner via a digital bus on a low-voltage section of the battery control unit. Individual cell voltages of individual battery cells or other measurement variables, such as temperatures of the individual cells or the control electronics thereof, are measured by cell size measuring devices and corresponding measurement data is transmitted to the battery control unit. In the prior art, this transmission typically occurs via an isolated or respectively galvanically separated low-voltage interface.        
The battery control unit typically monitors the cell voltage of each individual cell, the total voltage of the battery and the current which flows through the series circuit of the battery cells. The total system consisting of battery control unit and monitoring devices is referred to as the battery management system. Specially integrated circuits (ICs) are used for the cell voltage measurements, said ICs measuring the voltage of an associated cell. Such an IC can be provided for each cell; however, the cell voltages of a plurality of cells are typically measured with one IC, for example between 6 and 16 cells per IC. As a result, costs for the ICs can be saved. The measured voltage values are digitized and are transmitted to the receiver of the data by means of a special bus system, in which the voltage measuring devices are connected to one another in a chain and form a portion of the bus system. Such a bus system is generally referred to as a “daisy chain”. The bus runs not only in the interior of one or a plurality of ICs.
In order to measure the current through the series circuit of the battery cells, only one current converter is required in many cases because, in any case, this current flows in equal amounts through all of the cells unless the cells in a plurality of strings are connected in parallel to one another. A plurality of current sensors can then be provided. According to the prior art, the current sensors are connected to the receiver of the current values by means of another interface or respectively another bus.
In a battery monitoring system, in which the cell voltage values and current values are processed by the same receiver, for example a battery control unit, two different interfaces are then provided for the battery control unit. Either an additional voltage sensor and thus a third interface to the receiver of the data thereof, for example the battery control unit, is required to measure the high voltage; or the high voltage is measured directly by the receiver, for example the control device. This constellation in the prior art makes the synchronization of the scanning of individual voltage values, the high voltage value and current values (if required), which scanning takes place as simultaneously as possible, more difficult. The WIPO patent application WO2013/007617 discloses, for example, two separate buses for two different strings of voltage measuring devices.
The architecture of a battery management system according to the prior art is depicted in FIG. 1 in a simplified manner. A battery string consisting of battery cells connected to one another in series, for example up to 120 cells, is monitored by modular cell measuring modules, which each comprise a low-voltage measuring device. The measuring modules measure the voltage of each individual cell and detect the temperature of a battery cell and/or the associated electronics thereof. The measurement values are transmitted to the battery control unit via a common bus. According to the prior art, the topology of the bus interface is configured according to the daisy chain principle. A cell measuring module, which is situated at the end of the chain of cell measuring modules, is directly, i.e. not via other cell measuring modules, connected to the battery control unit. The further cell measuring modules are each connected to the chain by means of the precursors thereof (series circuit principle). Due to the voltage offset between the individual battery cells within the series circuit thereof, a special switching circuit, which carries out the necessary level conversion, is integrated into each of the cell measuring modules.
In order to measure the system voltages, a circuit section comprising an interface for high-voltage signals is provided in the battery control unit. The signals having high-voltage potential are transformed into further processed low-voltage signals, filtered and subsequently converted into a digital signal. The digital signal is (e.g. capacitively, inductively or optically) electrically isolated by means of a separating device and transmitted to the low-voltage section of the battery control unit and processed there.
In total, a plurality of interfaces to the battery control unit results, said interfaces being required to detect all of the necessary system variables. A considerable amount of effort and cost additionally arises when detecting all of the system variables in a temporally synchronous manner for the purpose of being further algorithmically processed.
According to the prior art, the use of an analog-to-digital converter of a microcontroller is also known, said converter constituting the battery control unit or a section thereof, in order to measure voltages or currents of battery cells or of the whole battery. The American patent application US 2006/0170389 discloses, for example, the use of an A/D converter comprising a multiplexer for measuring a plurality of voltages of battery cells. The American patent application US 2013/0175976 discloses the electrical isolation or galvanic separation of a CAN bus from a battery control system.
It was required to date to send a plurality of signals via a plurality of different bus systems to the corresponding measuring devices for each measurement with which the state of all the battery cells of the battery can be determined. To this end, a plurality of different commands having different protocols is required, which means increased effort and cost for the implementation of the process as well as increased computational effort for the execution of said process. This also applies equally to the commands for transmitting measurement signals from the measuring devices to the battery control unit.